The invention relates to a system and a method for starting an internal-combustion engine arranged in a vehicle. The following is provided for starting the internal-combustion engine: an electric machine designed for at least temporarily driving the internal-combustion engine, and a first storage unit designed for storing electric energy.
Internal-combustion engines of different constructions are currently used in automobile manufacturing. One characteristic in which the internal-combustion engines differ with respect to their construction is the type of the ignition initiation. There are self-igniting internal-combustion engines (diesel engines) and externally supplied ignition internal-combustion engines, the most wide-spread externally supplied ignition internal-combustion engine being the Otto engine. A further differentiating characteristic is the number of cylinders. In automobile manufacturing, internal-combustion engines are predominantly used which have three, four, six, eight or twelve cylinders.
So far, an individual starter engine and a pertaining individual energy supply have been developed or conceived for any type of internal-combustion engine: both components were individually designed as a function of the type of ignition initiation and of the number of cylinders. The reasons are the following: the different types of internal-combustion engines each make different demands on the ideal electric power which is consumed by the starter motor during the starting operation and/or the ideal electric current which flows through the starter motor during the starting operation. In addition, the ideal power and the ideal electric current vary for the respective type of internal-combustion engine as a function of the operating temperature of the internal-combustion engine. In the case of a cold start, the starter motor consumes a different electric power than in the case of a warm start.
A further aspect is the following. In the case of vehicles equipped with a so-called automatic start-stop system, as well as in the case of hybrid vehicles, a starting behavior is required which is modified compared with a conventional vehicle. With an automatic start-stop system, the internal-combustion engine is switched off when the vehicle is stopped. In the case of a hybrid vehicle, an internal-combustion engine as well as an electric machine are provided for the propulsion. The modified starting behavior is connected with new operating strategies which are contemplated or become necessary by means of these novel vehicles, and which lead to changed demands on the electric power consumed by the starter motor during the starting operation and on comfort during the starting operation.
In the case of a conventional vehicle, the starter motor and the pertaining energy supply are designed for the first start, or initial start, of the internal-combustion engine, which is first triggered after the driver enters the vehicle at the beginning of a trip. In the case of a first start, it is not necessary for the internal-combustion engine to provide a defined high torque within a very short time.
In the case of a vehicle with an automatic start-stop system, in addition to the first start, a restart and possibly an additional start of the internal combustion engine also have to be carried out. In the case of a restart as well as an additional start, there is at first no operative connection between the internal-combustion engine and the driven wheels of the vehicle, but it is immediately imminent. The restart and the additional start are caused by a control unit installed in the vehicle. A restart to be carried out is recognized when a start driving signal is present in an idle vehicle state (in the idle vehicle state, the vehicle has stopped and the internal-combustion engine has stopped or has a rotational engine speed between a rotational switch-off speed and the zero value). An additional start to be carried out is recognized when, in a moving state of the vehicle, an engine torque demand is present (in the moving state, the vehicle is driven and the internal-combustion engine has stopped or has a rotational engine speed between a rotational switch-off speed and the zero value).
In the case of the idle vehicle state as well as the moving vehicle state, it is the intention that the internal-combustion engine is either idle (rotational engine speed of zero) or is carrying out a diminishing rotational engine movement (rotational engine speed between the rotational switch-off speed and the zero value). In the idling vehicle state, the vehicle speed preferably should have a zero value. However, automatic start-stop systems are also contemplated, in the case of which a restart can be carried out when the vehicle is moving at a speed that is not too high, for example at 3 km/h or at 20 km/h. A restart to be carried out can therefore also be recognized when, in a conditional vehicle moving state, a start driving signal is present, in which case the conditional vehicle moving state will be present when the speed of the vehicle is lower than a threshold value which amounts to, for example, 3 km/h or 20 km/h.
In the moving state of the vehicle, the vehicle speed has an arbitrary value different from zero, which is preferably clearly higher than 20 km/h and, for example, at 50 km/h or 70 km/h or clearly higher values. The start driving signal represents an immediately imminent driving start of the vehicle which is to begin from the idle vehicle start. This should preferably be a driving start initiated by the driver. In this case, the start driving signal may, for example, be a signal that represents the actuation of the clutch pedal by the driver. However, as an alternative, the driving start may also be automated, thus initiated independently of the driver. The engine torque demand represents a torque which is to be adjusted by the internal-combustion engine in the present vehicle moving state in a driver-dependent or driver-independent manner. A torque to be adjusted in a driver-dependent manner occurs, for example, as a result of an actuation of the accelerator pedal by the driver. Here, the torque demand may therefore be a magnitude representing the accelerator pedal actuation. For example, a longitudinal control unit can generate a driver-independent engine torque demand, in which case, the longitudinal control system may, for example, be an adaptive cruise control. The switch-off rotational speed is that rotational engine speed of the internal-combustion engine which occurs when the internal-combustion engine is disconnected, i.e. during or immediately after the interruption of the operative connection with the driven wheels, for example, caused by actuating the clutch. In the first moment, the rotational switch-off speed can correspond to the rotational idling speed but, depending on the operation, may also temporarily be above the rotational idling speed.
The restart and the additional start of the internal-combustion engine differ from an initial start. During the restart, for example, at a traffic light, a large torque has to be provided by the internal-combustion engine within a very short time; the internal-combustion engine is started more rapidly than during the initial start. During the additional start of the internal-combustion engine in a moving state of the vehicle, the internal-combustion engine has to provide a torque correlating with the vehicle moving state within a very short time; a very fast “pulling-up” of the internal-combustion engine to a desired rotational driving speed is required (reflex start).
In the case of a hybrid vehicle, an additional start of the internal-combustion engine has to be carried out together with the first start. The statements made above with respect to a vehicle having an automatic start-stop system also apply here correspondingly.
These new operating strategies (additional start and/or restart) with the resulting modified starting behavior require a starter motor coordinated with the respective internal-combustion engine and a pertaining energy supply which are more efficient with respect to the components used in conventional vehicles. The components used in conventional vehicles therefore cannot simply be used in the novel vehicles.
A further aspect requiring the use of changed and therefore novel starter motors is the following: new drive architectures, as used, for example, in the case of micro- or mild-hybrid vehicles, specify new operating voltages for the starter motor. In the case of these drive concepts, the starter motor is supplied by way of a separate onboard power supply system whose voltage may be in the range of from above 12 V to 60 V, but may also amount to above 300 V. In this case, this voltage is above the voltage of a conventional onboard power supply system, which normally amounts to 12 V.
A further aspect requiring the development of novel starter motors is the use of electric energy storage devices which, in comparison to conventional lead batteries, can supply much higher short-circuit currents. One example are so-called supercapacitors which can provide short-circuit currents in the order of up to 1,500 A.
If the previous approach were used, while taking into account the above-indicated aspects, specifically the type of ignition initiation, the number of cylinders, including the taking-into-account of the operating temperature of the internal-combustion engine, the new operating strategies, the new drive architectures and the new electric energy storage devices, which all each make individual demands on the ideal electric power consumed by a starting motor during the starting operation and/or on the ideal electric current flowing through the starter motor during the starting operation, a large number of individually designed starting motors and pertaining energy supply systems would be required. In the case of a vehicle to which several of these aspects apply, particularly the aspects of new operating strategies, new drive architectures and new energy storage devices, in each case, while taking into account the operating temperature of the internal-combustion engine, this would have the result that such a vehicle would have to be equipped with a plurality of starting systems (starter motor and onboard power supply system) individualized with respect to the respective aspects. One example of a vehicle where this could be the case is a hybrid vehicle.
It is therefore an object of the present invention to further develop a system and a method of the initially mentioned type in order to, in the case of a vehicle, to which several aspects apply which each make individual demands on the ideal electric power drawn by a starter motor during the starting of an internal-combustion engine and/or on the ideal electric current flowing through the starter motor during the starting of an internal-combustion engine, instead of requiring a plurality of individualized starter motors or starter systems, have only a single starter motor or a single starter system. In particular, the use of already available, cost-effective direct-current starter motors should be possible. On the whole, a cost-effective, easily operable system requiring little space and/or a corresponding method are to be provided.
This and other objects are achieved by a system for starting an internal-combustion engine arranged in a vehicle, having an electric machine designed for at least temporarily driving the internal-combustion engine, and a first storage unit designed for storing electric energy. The system has an adjusting unit by which the electric machine can be connected with the first storage unit. The adjusting unit is designed for detecting at least one defined internal-combustion engine operating state and/or at least one defined vehicle operating state and, at least as a function of the detected internal-combustion engine operating state and/or the detected vehicle operating state, for adjusting an electric quantity which determines an electric power drawn from the first storage unit by the electric machine when driving the internal-combustion engine, or for itself adjusting the drawn electric power.
This object is further achieved by a method whereby the following steps take place in an adjusting unit by which the electric machine can be connected with the first storage unit: (i) detecting at least one defined internal-combustion engine operating state and/or at least one defined vehicle operating state, and (ii) adjusting an electric quantity which determines an electric power drawn by the electric machine from the first storage unit for driving the internal-combustion engine, or the drawn electric power itself, at least as a function of the detected internal-combustion engine operating state and/or of the detected vehicle operating state.
The system according to the invention and the method according to the invention are based on the following. With respect to the circuitry, an adjusting unit is inserted between the electric machine and the first storage unit. By way of this adjusting unit, an electric quantity, which determines an electric power drawn from the first storage unit during the driving of the internal-combustion engine, or the drawn power itself, can be adjusted. Thus, in the case of a vehicle to which several aspects apply, which each separately make individual demands on the ideal electric power which is consumed by a starter motor during the starting of an internal-combustion engine, the possibility is provided to directly or indirectly adjust the drawn and thereby consumed electric power, specifically according to the aspect that is valid at the current time or is to be taken into account in each case. The drawn electric power can therefore be adjusted corresponding to the respective aspect and can thereby be adapted to the correspondingly resulting starting demand. It thereby becomes possible, by use of a single starter motor or by use of a single starting system, to meet all demands on the drawn electric power and thus the start of the internal-combustion engine per se, which are defined or predefined by the different aspects to be used or to be taken into account for the respective vehicle.
The adjusting unit permits an adjusting or active varying of the electric power drawn from the first storage unit and thereby consumed by the electric machine or of the electric quantity that determines this power. As a result of the fact that the adjusting of the drawn electric power or of the electric quantity takes place at least as a function of an internal-combustion engine operating state and/or a vehicle operating state, an adaptation becomes possible at least to the different realities during the cold start and warm start as well as to the different realities of the respective new operating strategy. This permits the following approach to the development and conception of the electric machine: it is determined ahead of time in which internal-combustion engine operating state or vehicle operating state, or combination of both types of states, the highest-value electric power is consumed by the electric machine. The electric machine will then be designed for this electric power. The adjusting unit can then adjust the electric power drawn from the first storage unit for those internal-combustion engine operating states or vehicle operating states, or combinations of both types of states, in which the electric power of the highest value does not occur.
The adjusting unit represents a system connected on the input side by which the electric power drawn from the first storage unit and therefore consumed by the electric machine can be adjusted or limited.
In order to permit the above-mentioned adaptation, the adjusting unit preferably has at least one detection unit and a triggering unit. The detection unit is constructed for detecting at least one defined internal-combustion engine operating state and/or at least one defined vehicle operating state. The triggering unit is designed for setting, as a function of the detected internal-combustion engine operating state and/or of the detected vehicle operating state, the drawn electric power or that electric quantity which determines the drawn electric power.
If further pertinent values and/or parameters are detected or at least processed in the adjusting unit, an adaptation becomes possible of the drawn electric power to further aspects or to demands predefined by the latter; thus, for example, to the type of the ignition initiation, to the number of cylinders, to the type of the drive architecture to be used or to the type of the used electric energy storage devices.
Consequently, the adjusting unit is designed for limiting an electric current drawn by the electric machine from the first storage unit. The electric current is therefore the electric quantity to be adjusted, which determines the drawn electric power. In its functionality, the adjusting unit corresponds to an adjustable or controllable impedance. The drawn current can be easily and precisely adjusted, which is therefore correspondingly applicable to the drawn electric power. The electric machine can therefore be designed for the maximally possible electric current flowing through it, in which case, for those internal-combustion engine operating states or vehicle operating states, or combinations of the two types of states, in which this current does not occur, the current flowing through the electric machine is limited to a correspondingly lower value.
The electric machine has a number of stator windings, so that, in a further development of the above-mentioned measure, the adjusting unit is designed for limiting the electric current for the individual stator windings. This measure has the advantage that the electric power drawn by the electric machine or the electric current flowing through it can be adjusted particularly precisely.
In a further development of the invention, the adjusting unit is designed, at least over its partial periphery, for the implementation of a step-down converter functionality. For this purpose, the adjusting unit has, in its periphery relating to the power part, a switching element on the input side, particularly a MOSFET transistor and a recovery diode, in which case, instead of the recovery diode, an additional transistor can be used. Preferably, at least one of the stator windings, of which the electric machine has several, is used as a storage inductivity required for the implementation of the step-down converter. As a result of the combination of the components contained in the adjusting unit—this is either a switching element or a recovery diode or two switching elements—and the stator winding of the electric machine, a modified step-down converter is created which, compared to the classical step-down converter, has no filter capacitor. A step-down converter is a direct-voltage converter of a very simple and robust construction that works very reliably. It is distinguished by the fact that the voltage provided by it on the output side has a lower value than the voltage fed to it on the input side. The value of the voltage provided on the output side is defined by the controlled switching-on and -off of the switching element.
In the case of an electric machine used in a vehicle for propulsion, in the event of a propulsion, very high-value electric currents can flow through this electric machine. For this reason, the inductance required for the implementation of the step-down converter functionality has to be dimensioned to be correspondingly high. The inductance values of a correspondingly suitable inductance are in the order of several μH, preferably in the range of from 5 to 6 μH or even above. Storage inductances with inductance values above 6 μH have the advantage that the timing frequency for the operation of the step-down converter can be reduced, whereby the switching losses in the switching elements can be reduced. Such inductances have the disadvantage that they are not only large but also expensive. Here, the inventors now recognized that at least one of the stator windings present in the electric machine anyhow can be used as a storage inductance and, therefore, for the implementation of the step-down functionality. As a result, an independent large and expensive inductance to be provided additionally can be eliminated, which leads to low costs and reduces the space requirement. The electric machine preferably is a pinion starter motor whose armature inductance can be used for implementing the step-down converter functionality. The pinion starter motor is preferably constructed as a permanently excited direct-current motor. It may preferably be an electronically commutated direct-current motor.
By combining the components contained in the adjusting unit with the components of the electric machine, a step-down converter is obtained by which the above-mentioned electric quantity or the drawn electric power itself can be adjusted. In other words, in an interaction with the electric machine, by means of the adjusting unit, the above-mentioned electric quantity or the electric power itself can be adjusted. The modified step-down converter consists of spatially separated components, first components, which are contained in the adjusting unit and (switching elements and/or a recovery diode) and second components which are contained in the electric machine (stator winding).
In a further development of the invention, the adjusting unit is further designed for adjusting the electric quantity or the drawn electric power itself as a function of a value characterizing the internal-combustion engine. The characterizing quantity preferably is a value which characterizes the starting behavior of the internal-combustion engine, particularly the time-related behavior of the internal-combustion engine during the starting operation. This means that, as a function of the starting behavior of the internal-combustion engine, the electric power drawn during the starting operation by the electric machine from the first storage unit or the electric current flowing in this case through the electric machine is adjusted or limited. Advantageously, the adjusting or limiting takes place such that, for the current flowing through the respective stator winding of the electric machine, that current peak that follows the switch-on current peak has such a sufficiently high value that, within the starting operation, the first compression of the internal-combustion engine can take place completely because the internal-combustion engine will otherwise not start. The characterizing quantity is therefore an above-mentioned current peak, preferably a current value correlating with the above-mentioned current peak and/or a pertaining time value.
As an alternative or in addition, the characterizing quantity may also be a starting time to be observed, within which the internal-combustion engine has to have started. When driving the internal-combustion engine, from this starting time, the electric power to be drawn by the electric machine from the first storage unit for this purpose and therefore the electric power required for the driving of the internal-combustion engine, or the electric current flowing through the electric machine will be determined and adjusted or limited. As an alternative or in addition, the characterizing quantity may also be a torque of the internal-combustion engine which, during the starting operation, has to be overcome by the electric machine. As a function of this torque, a value is determined for the electric power to be generated for this purpose by the electric machine and therefore for the current flowing through the electric machine during the starting operation.
Independently of which value is used as the basis for determining a value for the electric power to be drawn by the electric machine from the first storage unit for driving the internal-combustion engine or for the current in this case flowing through the electric machine, as a function of this value, values are determined for duty factors by which semiconductor elements present in the adjusting unit are to be triggered in order to adjust or limit the demanded electric power or the demanded electric current.
Preferably, the characterizing quantity is a value which is determined ahead of time within the scope of an application and is stored or filed in the adjusting unit. Advantageously, when adjusting the electric quantity or the drawn electric power itself, a value representing the charging position of the first storage unit can be taken into account, this value preferably being the voltage applied to the first storage unit.
In a further development of the invention, a bridging unit, which can be activated, is provided, during whose activation, the electric machine, while bypassing the adjusting unit, is connected directly with the first storage unit and a second storage unit. This measure has the following advantage. For example, in the case of a cold starting, during the starting operation, extremely high currents flow through the electric machine, particularly when this starting operation is carried out at a very low ambient temperature. If the circuitry-related arrangement is now maintained, according to which the electric machine is connected by way of the adjusting unit with the first storage unit, the limitation functionality of the adjusting unit may have the effect that the extremely high currents required for the starting of the internal-combustion engine cannot occur. When now, by activating the bridging unit, the circuitry-related arrangement is disintegrated such that the electric machine is connected directly with the first storage unit or a further second storage unit, preferably a lead accumulator arranged in a 12 V onboard power supply system, the extremely high currents can be implemented because the limitation functionality of the adjusting unit has no effect. A corresponding approach may also be required during the first start in certain situations.
As mentioned above, the electric machine has a number of stator windings. Advantageously, the adjusting unit has a number of series-connected first and second semiconductor elements for each of the stator windings, the series connection having a center tap, to which the respective stator winding is connected. If the electric machine has three stator windings, the adjusting unit will have six semiconductor elements in its minimal configuration. Should all three first and three second semiconductor elements be transistors, preferably MOSFET transistors, the adjusting unit will contain a so-called B6 bridge by way of which the three stator windings are supplied with current. For this purpose, the adjusting unit is designed for triggering the first and second transistors connected in series for a stator winding in a complementary fashion corresponding to a predefined trigger pattern. Advantageously, the adjusting unit contains at least two series connections, preferably four series connections, for each of the stating windings. The series connection is connected parallel to one another. As a result the demanded high electric currents can be implemented.
In a further development of the invention, at least one smoothing filter is provided. This smoothing filter is preferably contained in the adjusting unit and is, for example, implemented as an LC section. By using a smoothing filter, the adjusting unit corresponds to the circuit diagram of a classical step-down converter with respect to its periphery concerning the power part. The smoothing filter has the function of damping possibly occurring voltage peaks and thereby smoothing the voltage applied on the output side of the adjusting unit. As a result, external power losses and disturbances in the input-side voltage of the step-down converter can be avoided. Furthermore, the wear at the brushes of the pinion starter motor are reduced by the use of the smoothing filter.
In a further development of the invention, the adjusting unit is further designed for limiting an electric voltage applied to the electric machine. This measure has the following advantage. If a vehicle is equipped with a new drive architecture, it has a separate onboard power supply system whose voltage is higher than the voltage of a conventional onboard power supply system. Based on the voltage of the separate onboard power supply system, it now becomes possible to generate a voltage of 12V, which corresponds to the value of a conventional onboard power supply system. It thereby becomes possible to supply an electric machine, which is designed for a 12 V onboard power supply system, with electric energy by way of the separate onboard power supply system.
It is understood that the above-mentioned characteristics and the characteristics to be explained in the following can be used not only in the respectively indicated combination but also in other combinations or alone without leaving the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.